Indexed on: 16 May '09Published on: 16 May '09Published in: Applied Physics A
This paper describes the fabrication of cobalt ferrite (CoFe2O4) nanostructures (in the form of nanofibers and nanoparticles) by the electrospinning method using a solution that contained poly(vinyl pyrrolidone) (PVP) and cheap Co and Fe nitrates as metal sources. The as-spun and calcined CoFe2O4/PVP composite samples were characterized by TG-DTA, X-ray diffraction, FT-IR, SEM and TEM, respectively. After calcination of the as-spun CoFe2O4/PVP composite nanofibers (fiber size of 320±48 nm in diameter) at 500, 600, and 800°C in air for 3 h with different heating rates of 5 or 20°C/min, either NiFe2O4 nanofibers of ∼10−200 nm in diameter or nanoparticles with particle sizes of ∼50−400 nm having a well-developed spinel structure were successfully obtained. The crystal structure and morphology of the nanofibers were influenced by the calcination temperature and heating rate. A faster heating rate allowed for a rapid removal of the PVP matrix and resulted in a complete change from fibrous structure to particle in the calcined CoFe2O4/PVP composite nanofibers. Room temperature magnetization results showed a ferromagnetic behavior of the calcined CoFe2O4/PVP composite nanofibers, having their hysteresis loops in the field range of ± 4500 and 3000 Oe for the samples calcined respectively with heating rates of 5 and 20°C/min. The values of the specific magnetization (Ms) at 10 kOe, remnant magnetization (Mr), Mr/Ms ratio, and coercive forces (Hc) are obtained from hysteresis loops. It was found that the values of Ms, Mr, Mr/Ms, and Hc depended strongly on morphology of the CoFe2O4 nanostructures.